Dragon Ball Z: The History of Trunks, known in Japan as Dragon Ball Z: Zetsubō e no Hankō!! Nokosareta Chō-Senshi Gohan to Trunks (ドラゴンボールZ 絶望への反抗!!残された超戦士・悟飯とトランクス, Doragon Bōru Zetto Zetsubō e no Hankō!! Nokosareta Chō-Senshi • Gohan to Torankusu?, lit. "Dragon Ball Z: Resistance to Despair!! The Remaining Super-Warriors, Gohan and Trunks"), is an hour-long TV-Special (#2) that is part of the Dragon Ball Z series of anime. Originally released in Japan on February 24, 1993, between episodes 174 and 175. Bridge Entertainment's title is Gohan and Trunks. It tells the story of Future Trunks. It is unique among Dragon Ball movies/specials since it is actually based from a brief chapter in the manga, called Trunks the History - The Lone Warrior. The special changes several key plot points for drama (such as that in the manga Trunks was capable of turning Super Saiyan before Gohan's death).

Source: Wikipedia